The present invention relates to a water disposal system and a method of disposing water for disposing water produced during power generation by a power generator, and a power generation apparatus using the water disposal system and the method of disposing water, for disposing water produced during power generation.
Fuel cell is a device which supplies a fuel gas, such as hydrogen, together with oxygen (air), and allows the fuel gas and oxygen to electrochemically react with each other to thereby generate electric power on a power generator. The fuel cell is much hopeful for applications to electric cars or hybrid vehicles, in a form of being mounted as a motive power source on vehicles including automobiles, and its structural features capable of facilitating weight reduction or downsizing have been promoting approaches of applying it not only to the current dry cell or rechargeable battery, but also to the field of electric communication such as portable devices, field of power tools, field of general home electric appliances, field of lighting, field of emergency non-interruptive power source and field of munitions.
One known configuration of the fuel cell is such as having a predetermined electrolyte film, which is typically a proton conductor film, provided between an anode as the hydrogen-side electrode and a cathode as the oxygen-side electrode, wherein each electrode configures a cell structure together with a catalyst layer containing a catalyst added so as to allow source materials supplied to each electrode to react, and a diffusion layer portion for guiding the reaction materials to the catalyst, and a plurality of this sort of cells are stacked. In thus-configured fuel cell, a dissociative reaction of hydrogen gas (H2) into a proton (H+) and an electron (e−) occurs. In the fuel cell, proton (H+) migrates from the anode side towards the cathode side through the proton conductor film, and at the same time electron (e−) migrates towards the cathode through a predetermined external circuit, so as to proceed a reaction of producing water from oxygen (air), proton (H+) and electron (e−), and this results in generation of a predetermined electromotive force.
In thus-configured fuel cell, it is necessary to smoothly feed the supplied source materials to the catalyst layer so as to allow the reaction to proceed. It is, however, known that the water produced at the cathode or water back-diffused through the proton conductor film towards the anode side interferes flow of the supplied source material such as hydrogen gas, or stagnates in air feed grooves for feeding oxygen (air), and this is causative of lowering in the power generation efficiency.
In order to remove the water, the fuel cell generally adopts a technique of blowing the water in its liquid form making use of flow rate of the gas, or a technique of discharging the water in its liquid form with the aid of gravity.
The fuel cell based on the technique of discharging the water in its liquid form with the aid of gravity is, however, not applicable to small-sized devices such as portable electronic devices, because placement of the device is limited. On the other hand, the technique of blowing the water in its liquid form is not practical because it is realizable only by using a large-sized pump. It is therefore necessary for the fuel cell to discharge the water in its liquid form by using a small-sized pump fan or to allow the water to dry with air, if it is desired to be applied to the small devices.
As a specific technique of discharging the water from the catalyst layer or from the diffusion layer, there is proposed a technique disclosed in Patent Document 1 (Japanese Patent Application Publication No. Hei 10-289723).
Patent Document 1 discloses a fuel cell having a cathode-side current collector composed of a synthetic member which includes a base having a carbon fiber skeleton, and a porous mixture layer formed in a hole owned by the base, wherein the porous mixture layer is formed by firing a mixed paste of a water-repellent second filler and a first filler having a water repellency smaller than that of the second filler, and at least either one of the cathode-side current collector and anode-side current collector has water moving means for moving the water from the interface between itself and the electrode in contact therewith towards the back side of the current collector. It is explained that this fuel cell is advantageous in that the gas supply to the cathode will not be interfered, because the reaction water generated at the cathode can move through a path formed by grains of the first filler sequentially arranged in the thickness-wise direction of the current collector.
Other techniques of ensuring the gas flow by discharging the water from the air supply groove are proposed in Patent Document 2 (Japanese Patent Application Publication No. Hei 11-97041) and Patent Document 3 (Japanese Patent Application Publication No. 2001-11032).
Patent Document 2 discloses a solid-polymer-type fuel cell in which part of wall surface of the supply groove on the anode side are subjected to water-repellent treatment and hydrophilization treatment so as to form a water-repellent region and a hydrophilic region. It is explained that this solid-polymer-type fuel cell is successful in ensuring a path of the gas by forming the water-repellent region and hydrophilic region.
Patent Document 3 discloses a polymer-electrolyte-type fuel cell having a flow path for removing water, provided on at least any one of an anode, a cathode, and a pair of separators having, formed thereon, the supply grooves for supplying the gas to the anode and cathode. It is explained that this polymer-electrolyte-type fuel cell is successful in separating the water discharge and gas flow by disposing the flow path for removing water generated on the cathode side, and in avoiding clogging of the gas flow path.
The aforementioned technique described in Patent Document 1, however, suffers from a problem in that the water cannot completely be discharged from the diffusion layer to the external, and the water stayed in the internal becomes water droplets to thereby interfere the gas supply to the catalyst layer. The technique also raises a problem in that the water interferes flow of the source materials also on the anode side, because the amount of water back-diffused through the proton conductor film towards the anode side increases unless otherwise the water generated on the cathode side is successfully discharged to the external.
The water in problem may be discharged as being carried by a gas flow under control of pressure or flow rate of oxygen or air at the cathode, but it is difficult for flat-type or small-sized power generation cells, having a cathode often configured as of open air type, to discharge the water as being carried by the gas flow under control of pressure and flow rate of the gas. In particular for the case where this sort of power generation cell is mounted on any portable electronic devices, it is difficult to newly add a device for controlling the pressure or flow rate of the gas for disposing the water, so that the generated water, diffused in a form of droplets, may be causative of malfunctions due to water scattering to the peripheral devices.
Other possible methods may be such as blowing the water with the aid of some external device or naturally-occurred air flow, or discharging the water assisted by the self weight of the water droplets. It is, however, anticipated that these methods may undesirably result in scattering of the released water droplets towards unintended places, unless the device is directed within a predetermined range with respect to the air flow or gravity. Self-contained configuration of the power generation cell into a predetermined device raises problems not only in degradation in performances of the fuel cell, but also in releasing of the water per se in the device.
There is an idea of allowing the generated water droplets to flow along pipes, grooves or the like to thereby recover the water droplets in a predetermined site, but this inevitably requires an additional function of supplying energy for the recovery, against expectations for downsizing and improvement in efficiency of the device. For example in the technique described in Patent Document 4 (Japanese Patent Application Publication No. Hei 9-213359) in which the water generated at the cathode is recovered and used for moistening the anode, amount of generated water increases as the duration of time of power generation becomes longer, and the water must finally be disposed.
The aforementioned technique described in the Patent Document 2, in which the water droplets are discharged through a long air supply groove for supplying the air without being assisted by gravity, was suffering from a problem of needing a large-sized pump.
The aforementioned technique described in the Patent Document 3 was suffering from a problem in that the water entered the flow path for removing water may be discharged, but the water entered the air supply groove cannot be discharged at all.